DESCRIPTION:(from applicant's abstract) The long-term goal of this research is to understand the basic computational and control principles which the central nervous system uses to generate functional behavior. Some fundamental principles are implicit in the interaction of the central controller with its peripheral effectors, most importantly muscles. The motor commands of the nervous system and the peripheral response characteristics of the neuromuscular system must be mutually matched for optimal performance. In many systems this matching is accomplished by peripheral modulation which dynamically tunes the properties of the muscle so as to enable it to perform the behavior being commanded by the nervous system. But, although set up as part of the behavior, the modulation generally has much slower dynamics than those of the behavior. In effect, the modulatory state represents a memory, maintained peripherally in the muscle, of past behavior. This memory then prepares the muscle to perform future behavior. It facilitates performance especially of the same kind of behavior as in the past, but may complicate performance if the nervous system commands a different behavior without its presence into account. This peripheral memory and its consequences for control of motor performance and behavior by the nervous system will be studied in a well known, experimentally advantageous model neuromuscular system. The system participates in several behaviors and exhibits a rich variety of neuromuscular modulation on a wide range of time scales. Preliminary studies demonstrate prominent peripheral memory in the system. A strategy combining experiments with mathematical modeling will be used to address the following questions: What motor commands does the nervous system send in the different behaviors? What corresponding modulation occurs? How do the commands and modulation interact to produce functional movement? How does the functional movement change when on the one hand the motor commands, and on the other hand the modulation, are altered? Altogether, this work will test a two-part hypothesis, reflecting the mutual interdependence of controller and effector: that the peripheral memory is required for smooth, efficient integration of successive cycles of a behavior and even for transitions from one behavior to another; but that, at the same time, its existence requires modification of the commands sent by the central nervous system.